The present invention relates to a radio transmitter-receiver of so called a simultaneous transmitting and receiving system, capable of receiving a downstream radio signal transmitted from a base station while transmitting an upstream radio signal having amplitude variation components, such as a mobile terminal apparatus employing the CDMA (Code Division Multiple Access) scheme.
Recently, a cellular radio communications system has been rapidly widespread in accordance with the increase in the needs for the mobile communications and the development of the communications techniques.
A mobile terminal apparatus used in the cellular radio communications system, for example, receives a radio frequency signal transmitted from a base station, by an antenna, inputs the signal to a receiving radio-frequency unit via an antenna duplexer, high-frequency-amplifies the signal, removes unnecessary waves outside the receiving band from the signal, converts the signal to an intermediate frequency signal, demodulates the intermediate frequency signal by a demodulator, and converts the signal into a baseband signal. The transmitting baseband signal is subjected to a predetermined signal process, input to a modulator, which modulates a carrier wave signal. The modulated carrier wave signal is converted into a radio frequency by a transmitting radio-frequency circuit and amplified to a predetermined transmitting power, and transmitted to the base station from the antenna via the duplexer.
Incidentally, the receiving radio-frequency unit uses a low noise amplifier as a radio-frequency amplifier. In a conventional analog mobile terminal apparatus employing the FM scheme as its modulation scheme, for example, the distortion characteristics of the low-noise amplifier is generally set to be such that the input tertiary interception point (IIP3) can be about xe2x88x923 [dBm], at which the apparatus can bear the mutual modulation disturbance generated by adjacent and the following adjacent channels. In this case, the low-noise amplifier can be implemented with the consumed current of a few [mA].
In the mobile terminal apparatus employing the CDMA scheme, however, its own transmitting wave has amplitude variation components as shown in, for example, FIG. 1. For this reason, when a narrow-band disturbance tone signal in the analog cellular system using a near-field band of the CDMA cellular system exists near the desired receiving wave, the amplitude variation components of its own transmitting wave which cannot be attenuated by the duplexer causes the cross modulation resulting from the tertiary distortion of the low-noise amplifier to be generated, and overlap the disturbance tone signal as shown in FIG. 2, and part of it is added to the receiving band as interference.
The CDMA cellular system employs what is called open-loop transmission power control, which allows the transmitting signal power of the mobile terminal apparatus to be increased when the mobile terminal apparatus is remote from the base station and when the received signal level is low. When the mobile terminal apparatus exists in a place where the received signal level is low, such a case where the mobile terminal apparatus exists in, for example, a fringe area of a cell, deterioration of the receiving characteristics is accelerated because of the interference caused by the cross modulation effect, which may cause the communications to be interrupted in a worst case.
To solve this problem, the IIP3 of the low-noise amplifier provided in the receiving radio-frequency unit needs to be set at about 5-7 dB. In order to implement this, however, the consumed current needs to be increased to about 10 to about 20 [mA], and this will cause the standby time of the CDMA mobile terminal apparatus to be made remarkably shorter, which is not very preferable.
On the other hand, some measures to be taken, i.e. further increasing the attenuation amount of the transmitting frequency band on the receiving side of the duplexer and further lowering the signal level at which its own transmitting wave is input to the receiving radio-frequency unit, can be considered. With these measures, however, the duplexer is excessively large, which may disturb miniaturization of the mobile terminal apparatus and the reduction of the weight thereof.
As described above, in the radio transmitter-receiver for simultaneously transmitting/receiving the radio signal having the amplitude variation components, such as the mobile terminal apparatus used in the CDMA cellular system, the interference to the receiving band, which results from the cross modulation between the near-field disturbance tone signal of the desired receiving wave and its own transmitting wave, occurs and therefore, some measures need to be taken. According to the conventionally considered measures, however, the standby time is shortened by increasing the consumed current of the receiving radio-frequency unit, and the radio transmitter-receiver is made larger by making the duplexer larger, and thus, the effective measures have been desired.
The present invention is accomplished in consideration of the above circumstances, and its object is to provide a radio receiver, a receiving radio-frequency unit thereof, and a control unit, capable of preventing deterioration of the receiving sensitivity caused by its own transmitting wave and the disturbance wave as well as restricting the increase in the current consumption of the receiving radio-frequency unit, and thus extending the standby time or communications time with preferable receiving distortion characteristics.
According to one aspect of the present invention, there is provided a radio transmitter-receiver for simultaneously transmitting/receiving a radio signal including an amplitude variation component, comprising: a receiving radio-frequency unit having a first operation mode in which an operation is executed at a predetermined first current consumption value and a predetermined first distortion characteristics, and a second operation mode in which an operation is executed at a second current consumption value larger than the first current consumption value and a second distortion characteristics having less distortion than the first distortion characteristics; and a mode changing control means allowing the receiving radio-frequency unit to be operated in the second operation mode in a period in which the radio signal is transmitted, or in the first operation mode in a period in which the radio signal is not transmitted.
Therefore, according to the present invention, since the receiving radio-frequency unit is operated in the low-distortion mode, in the period in which the radio signal is transmitted, the deterioration of the receiving sensitivity which is caused by the interference to the receiving band resulting from the cross modulation between the near disturbance wave of the desired receiving wave and its own transmitting wave, is suppressed, and the receiving distortion characteristics can be thereby kept preferable.
On the other hand, since the receiving radio-frequency unit is operated in the low current consumption mode, in the non-transmission period during which occurrence of the cross modulation as the standby period needs not to be considered, the current consumption of the receiving radio-frequency unit is reduced and thereby the standby time can be extended.
That is, according to the present invention, the standby time can be extended while the receiving distortion characteristics at the transmitting/receiving operation are kept preferable.
The receiving radio-frequency unit may comprise an amplification means for amplifying a signal received by an antenna, and the mode changing control means may change an operation mode of the amplification means.
Further, the receiving radio-frequency unit may comprise an amplification means for amplifying a signal received by an antenna and a mixer means for mixing the output from the amplification means and the receiving local oscillation signal, and mode changing control means may change the operation modes of the amplification means and the mixer means.
According to another aspect of the present invention, there is provided a radio transmitter-receiver wherein, where the radio transmitter-receiver transmits a radio signal intermittently, the mode changing control means allows the receiving radio-frequency unit to be operated in the second operation mode in a period in which intermittent transmission of the radio signal is being operated and a transmitting wave is transmitted actually, or in the first operation mode in a period in which the intermittent transmission of the radio signal is being operated and the transmission of the transmitting wave is stopped.
With this operation, even in the transmitting period, the receiving radio-frequency unit is operated at the low current consumption mode while the transmitting wave is not transmitted due to the intermittent transmission. For this reason, the period to operate in the low distortion mode in which the consumed current is comparatively large, is further shortened and thereby the average consumed current is further decreased, which allows the continuous communication time to be extended.
According to the other aspect of the present invention, there is provided a radio transmitter-receiver wherein the mode changing control means allows the receiving radio-frequency unit to be operated in the second operation mode in a period in which the radio signal is transmitted and a receiving level of the radio signal is lower than a predetermined threshold value, or in the first operation mode in a period in which the radio signal is transmitted and the receiving level of the radio signal is equal to or higher than a predetermined threshold value.
That is, a mobile terminal apparatus used in the CDMA cellular radio system generally employs what is called an open-loop control of the transmitting level, which allows the transmitting level of the upstream radio signal to be made higher when the receiving level of the downstream radio signal arriving from the base station is lowered. In a case where such a control is executed, the transmitting level of the upstream radio signal is made higher when the receiving level of the downstream radio signal is low, and therefore, the receiving distortion characteristics can be easily deteriorated because of the cross modulation. Thus, in this case, the receiving radio-frequency unit is operated in the low distortion mode. With this operation, the receiving distortion characteristics of the receiving radio-frequency unit can be kept preferable though the transmitting level is high.
On the other hand, the transmitting level of the upstream radio signal is set to be low when the receiving level of the downstream radio signal is high, and therefore, the receiving distortion characteristics caused by the cross modulation is hardly deteriorated. Thus, in this case, the receiving radio-frequency unit is operated in the low current consumption mode. With this operation, the average value of the consumed current of the receiving radio-frequency unit in the transmitting period is lowered and thereby the continuous communication period is extended.
According to the other aspect of the present invention, there is provided a radio transmitter-receiver wherein the mode changing control means allows the receiving radio-frequency unit to be operated in the second operation mode in a period in which the radio signal is transmitted and the transmitting level thereof is equal to or higher than a predetermined transmitting level, or in the first operation mode in a period in which the radio signal is transmitted and the transmitting level thereof is lower than the predetermined transmitting level.
With this structure, the receiving radio-frequency unit is operated in the low current consumption mode when the transmitting level is low, in a case of employing the aforementioned open-loop control is employed and, of course, in a case of employing the closed-loop control which allows the transmitting level of the upstream radio signal to be variably controlled in accordance with the instruction from the base station. For this reason, the average value of the consumed current of the receiving radio-frequency unit in the transmitting period is lowered and thereby the continuous communication period can be extended.
According to the other aspect of the present invention, there is provided a receiving radio-frequency unit wherein a first active circuit section being operated at a predetermined first current consumption value and a predetermined first distortion characteristics, and a second active circuit section having the same function as the first active circuit section, and being operated at a second current consumption value larger than the first current consumption value and a second distortion characteristics having less distortion than the first distortion characteristics, are provided in parallel; and a switching circuit section allows the second active circuit section to be operated selectively in a period in which the radio signal is transmitted, or allowing the first active circuit section to be operated selectively in a period in which the radio signal is not transmitted.
According to this structure, the receiving radio-frequency unit of the present invention can be implemented comparatively simply.
Each of the first and second active circuit sections may comprise an amplification means for amplifying the signal received by the antenna.
According to the other aspect of the present invention, there is provided a receiving radio-frequency unit wherein only one active circuit section having a predetermined radio signal receiving function is provided; and a bias supply switching circuit section supplies a first bias current allowing the active circuit section to be operated at a predetermined first current consumption value and a predetermined first distortion characteristics, in a period in which the radio signal is transmitted, and also supplies a second bias current allowing the active circuit section to be operated at a second current consumption value larger than the first current consumption value and a second distortion characteristics having less distortion than the first distortion characteristics, in a period in which the radio signal is not transmitted.
According to this structure, the active circuit of the receiving radio-frequency unit can be constituted in one system except for the bias circuit portion, which allows the structure of the receiving radio-frequency unit to be miniaturized.
The active circuit section may comprise the amplification means for amplifying a signal received by an antenna, and the bias supply changing circuit section may supply the first or second bias current to the amplification means.
In addition, an isolator may be provided between the active circuit section and a front-stage circuit for inputting the radio signal to the active circuit section. With this structure, the input impedance variation occurring together with the changing of the bias currents of the active circuit section can be prevented from bringing its influence to the front-stage circuit, by the isolator, and thereby the frequency characteristics of the front-stage circuit can be prevented from varying.
Further, in the radio transmitter-receiver employing the open-loop control of the transmitting level, where variation components caused by changing of the modes of the receiving radio-frequency unit, that is, changing of the active circuit and changing of the supply of the bias current is generated in the transmitting level control signal generated on the basis of the output signal level of the receiving radio-frequency unit during the above-mentioned open-loop transmission control, the variation components may be canceled by the variation suppressing means. With this structure, the variation in the transmitting level resulting from the gain variation of the active circuit in the receiving radio-frequency unit can be canceled, which allows the transmitting level error of the upstream radio signal to be reduced and also allows unnecessary current consumption in the transmitting radio-frequency circuit to be reduced.
According to the other aspect of the present invention, there is provided a radio transmitter-receiver wherein, in a case where the radio transmitter-receiver comprises the mode designation input means for allowing the user to designate and input the first operation mode of the low current consumption type and the second operation mode of the low distortion type in the receiving radio-frequency unit, when the mode is not designated by the mode designation input means, the receiving radio-frequency unit is operated in the second operation mode in a period in which the radio signal is transmitted, or in the first operation mode in a period in which the radio signal is not transmitted; and when the first or second operation mode is designated and input by the mode designation input means, the receiving radio-frequency unit is operated at any time in the designated and input operation mode.
According to the present invention, when the user designates, for example, the low current consumption mode, the receiving radio-frequency unit is always operated in the low current consumption mode and thereby usage can be selected while considering the extension of the communication period and the standby period with priority. This is effective when, for example, little capacitance remains in the battery of the radio transmitter-receiver. On the other hand, when the user designates, for example, the low distortion mode, the receiving radio-frequency unit is always operated in the low distortion mode, and thereby the user can use it by considering the communication quality with priority. This is effective when, for example, it is difficult to listen to the voice of the communication partner.